The SD and BD engines were not fond of high RPM's. They don't like much over 3600 RPM, with 4000 rpm probably being an absolute maximum. The SD in particular had a reputation of dropping valves when operated at higher RPM's.
BUT...
The C-221, C-263, C-291, and C-301 farm tractor engines were VERY similar to the SD and BD truck engines...and tractor pullers have built them to hold together at around 6000 rpm. BUT that's a pretty specialized application, and those tractors are only running wide open for 300 feet at a time.
I've been told that Sonny at Bullet Cams knows a bit about what it takes to build one of these sixes to run. The website is
http://bulletcams.com/ . I've also heard that Jeff at Murphy Motor Service knows his way around these tractor engines...so some of the tech should be transferable to the truck engine as well. Their website is
http://www.murphysmotorservice.com/ .
And Kevin here on this site has some experience with Keystone Turbo; that's his truck in the photos here on their website:
http://www.keystoneturbollc.com/id80.html .
These sites, and a call to Sonny, should head you in the direction you're talking of. And if you go there...bring money. LOTS of money.